Computer-based approaches have been utilized to assign a classification to one or more documents such as emails or other communications. Generally, a classification of a document indicates a category or “vertical” associated with content of the document. Some approaches utilize a classifier that has been trained utilizing supervised learning techniques. Such supervised learning techniques rely on a training set of labeled documents that have been labeled as being associated with the classification. In some situations it may be impractical or impossible to obtain a large enough quantity of labeled documents for desired supervised training of a classifier. For example, privacy considerations may prevent many emails and other private documents from being provided for human review and labeling.